Humidification arrangement for a respiratory apparatus

ABSTRACT

A humidifying apparatus utilizing a semi-permeable membrane portion within a gas conduit where the direction of gas flow within a central lumen is given by an arrow. The humidification apparatus has a helical configuration for the semi-permeable membrane portion, a structural reinforcing member or members, a water channel and a heating element. The helical configuration of an outer wall may be similar to conventional conduits that are in common use in respiratory apparatus. Thus the humidification apparatus may be readily substituted into existing respiratory device by exchanging the gas conduit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/449,355, filed Aug. 4, 2009, now pending, which is the U.S. nationalphase of International Application No. PCT/AU2008/000145, filed Feb. 6,2008, which designated the U.S. and claims priority to AU ApplicationNo. 2007900653 filed Feb. 9, 2007, the entire contents of each of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to humidification arrangements used tocontrol the humidity of breathable gases used in all forms ofrespiratory apparatus ventilation systems including invasive andnon-invasive ventilation, Continuous Positive Airway Pressure (CPAP),Bilevel therapy and treatment for sleep disordered breathing (SDB)conditions such as Obstructive Sleep Apnea (OSA), and for various otherrespiratory disorders and diseases.

2. Description of the Art

Respiratory apparatus commonly have means to alter the humidity of thebreathable gas in order to reduce drying of the patient's airway andconsequent patient discomfort and associated complications. The use of ahumidifier placed between the positive airway pressure (PAP) device (orflow generator) and the patient mask, produces humidified gas thatminimizes drying of the nasal mucosa and increases patient airwaycomfort.

Many humidifiers types have been proposed, including humidifiers thatare either integrated with or configured to be coupled to the relevantrespiratory apparatus. While passive humidifiers can provide somerelief, generally a heated humidifier is required to provide sufficienthumidity and temperature to the air so that patient will be comfortable.

Humidifiers typically comprise a water tub having a capacity of severalhundred millilitres, a heating element for heating the water in the tub,a control to enable the level of humidification to be varied, a gasinlet to receive gas from the PAP device, and a gas outlet adapted to beconnected to a gas conduit that delivers the humidified pressurized gasto the patient's mask.

However such a humidifier arrangement has a limited area of interactionbetween the surface of the water in the tub and the gas flowing above sothat the capacity to deliver a high absolute humidity rapidly islimited. In addition the humidified air may cool on its path along theconduit from the humidifier to the patient, leading to the phenomenon of“rain-out”, or condensation, forming on the inside of the conduit.

Tub-of-water humidifiers are also vulnerable to liquid water spillage ifthey are not maintained in the vertical. Spillage of liquid water caneither travel into the gas conduit to the patient or back into the PAPdevice and associated electronics or deplete the reservoir ofhumidifying water. In either of the cases the spillage of water isundesirable.

Several references describe humidification arrangements associated withthe gas conduit between the blower or PAP device and the patient mask.These arrangements have consisted of discrete in-line units, tubes ofwater within the conduit or re-vaporization of water condensate in thegas conduit.

U.S. Pat. No. 4,146,597, U.S. Pat. No. 4,861,523, U.S. Pat. No.5,367,604 and U.S. Pat. No. 6,010,118 disclose the use of a discretein-line unit placed somewhere along the gas conduit to the patient.However such discrete humidification units have the disadvantages ofbeing bulky to the patient and impeding the free movement of the gasconduit as the patient moves.

Another humidification scheme is to have a water source enclosed withina tube of a semi-permeable membrane which is then inserted into the gasconduit. The tube may also incorporate heating elements to aid in thegeneration of water vapour. Examples of such prior art are U.S. Pat. No.3,871,373, U.S. Pat. No. 4,708,831 and U.S. Pat. No. 6,201,223.

Another example is the use of many tubes that are inserted into the gasconduit, U.S. Pat. No. 4,146,597, U.S. Pat. No. 6,394,084, U.S. Pat. No.6,557,551 and U.S. Pat. No. 6,877,510. The disadvantage of sucharrangements is the impediment to gas flow by the inserted tubes withinthe gas conduit to the patient. The tubes may also contribute to thecleaning burden within the gas conduit.

U.S. Pat. No. 6,662,802 describes an arrangement for collection of watercondensation within the gas conduit and then its re-vaporisation intothe gas flow, to reduce the effect of condensation within the gasconduit and to restore the humidity in the gas conduit. However, theapparatus does not have the capacity to increase the absolute humiditybeyond what can be gathered as a water source from the condensate in thegas conduit. That is, the arrangement cannot increase the absolutehumidity, merely restore it to the absolute humidity at which the gas issupplied to the conduit.

None of these prior art devices provides an entirely satisfactorysolution to the provision of humidified breathable gas to the patient,nor to ease of construction and hygiene requirements for ahumidification apparatus.

SUMMARY OF THE INVENTION

The present invention aims to provide an alternative humidifierapparatus which overcomes or ameliorates the disadvantages of the priorart, or at least provides a useful choice.

In one form, the invention provides a flexible gas conduit fordelivering breathable gas from a PAP device to a patient interface, suchas a mask, including a lumen for transport of the breathable gas and aconduit wall including a humidification apparatus.

Preferably, the humidification apparatus comprises a semi-permeablemembrane portion which provides a portion of the inner wall between thegas flow within the lumen of the gas conduit and a water channel in thegas conduit. The semi-permeable membrane portion has the characteristicof allowing water vapour to pass through it but not liquid water. Watervapour passing through the semi-permeable membrane portion may then beentrained into the gas flow to the patient interface.

In an alternate form, the humidification apparatus of the invention maycomprise a wick and/or capillary action device which is associated withone or more portions of the inner wall of the gas conduit. The wickand/or capillary action device provides water for vaporisation into thegas flow passing through the gas conduit.

A further form of the invention provides a heater which is in thermalcontact with the humidification apparatus. The heater may be used toincrease the rate of vaporisation of the water within the humidificationapparatus.

Optionally, the humidification apparatus and heater may each be dividedinto one or more separate portions along the gas conduit. The separateportions of each means may be separately controlled.

Further forms of the invention include a method of humidifyingbreathable gas being supplied to a patient by respiratory apparatus, andthe combination of respiratory apparatus with a gas conduitincorporating humidifying apparatus as described herein.

Further forms of the invention are as set out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further preferred embodiments of the invention will now be describedwith reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of the PAP device, gas conduit as thehumidifying apparatus and the patient mask, in an embodiment of thepresent invention.

FIG. 2 is an enlarged transverse sectional view taken along the lines2-2 in FIG. 1, which illustrates an embodiment of the humidificationapparatus using water channels.

FIG. 3 is an alternative embodiment of FIG. 2 using multiple water tubesto form the inner wall of the gas conduit.

FIG. 4 is an isometric view illustrating an alternative embodiment toFIG. 2.

FIG. 5 is longitudinal sectional view taken along the lines 5-5 in FIG.4.

FIG. 6 is an alternative embodiment of FIG. 2, where a wick device isused in the humidification apparatus.

FIG. 7 is a circuit diagram of a heating control circuit employing a PTCthermistor control.

FIG. 8 is a cut-away perspective view of an alternative embodiment ofthe humidification apparatus where the wick device is located in thewater channel.

FIG. 9 is a longitudinal cross-sectional view of FIG. 8 along the lines9-9.

FIG. 10 schematically shows the humidification apparatus of FIG. 8connected with a PAP device and a cut-away representation of a waterreservoir.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a PAP device 10 which produces a gas flow andgas pressure that is fed into a flexible conduit 12. The flexible gasconduit 12 has a central lumen 13 (FIG. 2) for conveying the gas flow tothe patient mask 14 which is attached to the upper and/or lower airwayof the patient or alternatively directly into the patient's airway via atracheostomy tube. The humidifying apparatus of the present embodimentsconsists of the gas conduit 12 incorporating a humidification apparatuswithin it.

Semi-Permeable Membrane Portion

FIG. 2 illustrates a cross-sectional view of a humidification apparatuswithin a flexible gas conduit 12, according to a first embodiment. Thehumidification apparatus may have one or more semi-permeable membraneportions 16 which forms one or more portions of an inner wall of adouble-walled conduit 12 and which allows water vapour to pass throughthe membrane but not liquid water. The inner wall of the double walledconduit 12 may be made entirely of semi permeable membrane portions 16.

The semi-permeable membrane portion may be formed of a material whichhas fine pores or perforations and may also be hydrophobic, the finenessof the porosity or the perforations and/or the degree of hydrophobic tohydrophilic nature being adapted to result in the desired effect ofsemi-permeability.

Some examples of semi-permeable membrane materials with suitablecharacteristics and which are suitably flexible for use in the presentinvention include:

-   -   Porous polytetrafluroethylene (PTFE) materials, microporous PTFE        membranes and expanded PTFE (ePTFE) from Gore-tex® , W.I., Gore        & Associates, Inc of Maryland USA.    -   Tyvek® spun polyethylene sheet material from DuPont.    -   PTFE mesh sold as Fluorcarbon SPECTRA/MESH® by Spectrum        Laboratories of Rancho Dominguez, Calif. USA.    -   Fibrous membranes consisting of auxetic fibres (fibres with a        negative Poisson's Ratio).        A more comprehensive discussion of suitable semi-permeable        membrane materials is included in Patent Application No. WO        2006/069415 A1 “Respiratory Mask having Gas Washout Vent and Gas        Washout Vent Assembly for Respiratory Mask”, the contents of        which are incorporated herein by reference.

The semi-permeable membrane portion 16 forms the inner wall, adjacent tothe central lumen 13, of the flexible gas conduit 12 as shown in FIG. 2.

Structural reinforcing members 18 extend along the wall of the conduitto provide support to the semi-permeable membrane portion 16 and to theouter wall 20 of the gas conduit 12. The reinforcing members 18 alsohave a spacing function in order that a water channel 22 (or waterdelivery passage) is formed within the gas conduit 12 between thesemi-permeable membrane portion 16 and the outer wall 20. The structuralreinforcing members and/or spacers 18 may be longitudinal, as shown inFIGS. 2 and 3, or helical as illustrated in FIGS. 4 and 5 or acombination of these arrangements, but in all the arrangements thereinforcing supports 18 allows the gas conduit 12 to flex to a degreesufficient to allow its use as a flexible gas conduit.

Associated with the water channel 22 there may also be placed one ormore heater/s 24 as shown in FIG. 2. The heater 24 is in thermal contactwith the water in the water channel 22 and in electrical contact withthe electronics associated with the PAP device 10. The heater 24 heatsthe water in the water channel in order to increase the production ofwater vapour, which migrates through the semi-permeable membrane portion16 to mix with the gas flow within the lumen 13 of the gas conduit 12and thus raise the humidity of the gas travelling through the gasconduit 12.

The heater 24 may consist of a heating element which may for exampleconsist of a resistive conductor. The conductor may consist of multipleresistive conductors connected to each other in series, parallel orsegmented along the length of the gas conduit 12 in order to allowuniform, variable and/or sectional heating along the conduit.

Such a heating element 24 may be controlled by one or more positivetemperature coefficient (PTC) thermistors 32 electrically in series withthe power supply 34 and the resistive conductors 24, for example asshown in the circuit diagram of FIG. 7. The PTC thermistor 32 operatesto decrease heating as the temperature increases towards a desiredtemperature for the gas flow. The PTC thermistor 32 may be locatedpreferably at the end of the gas conduit 12 towards or at the patient'smask 14, and in one embodiment is located on or incorporated in a cuffof the conduit for connection of the patient interface/mask.

The thermistor 32 may consist of a discrete semiconductor component suchas a “bead” thermistor. Alternatively the function of the thermistor 32may be served by a conductive thermoplastic elastomer (PTC-TPE) with PTCelectrical properties. The PTC-TPE can be moulded into a form to fit thepatient end of the gas conduit 12 as a cuff portion or a portion of thepatient mask 14. Therefore the temperature sensor may be integral to thegas conduit 12 or patient mask 14 or any other associated component.

The heater 24 may be a flexible tape heater as described in the PCTPatent Application No. PCT/AU2007/001715 “Humidifier for a RespiratoryApparatus”, the contents of which are incorporated herein by reference.

In one embodiment, the heating element 24 is formed by printed circuittechniques applied to a surface of a flexible substrate such as siliconerubber, all-polyimide or PTFE. Included in the printed circuittechniques which may be used are etched foil, printing and vacuumdeposition techniques. The Thermofoil™ range of the type of flexibleheaters by Minco of Minneapolis USA, described at www.minco.com, areexamples of commercially available strip heaters which may be modifiedfor use in the present application.

Alternatively, the flexible tape heater may be formed as a heatingelement, for example in the form of a resistive wire or ribbon,laminated between tapes of polycarbonate or other suitable plastics film

The outer wall 20 of the gas conduit 12 may provide, protection,insulation and additional structural support to the other elements ofthe humidifying apparatus but still allows the gas conduit 12 to flex inuse.

An alternative embodiment of the humidification apparatus is shown intransverse cross section in FIG. 3. In this embodiment water tubes 26are formed of semi-permeable membrane portion, for example of thematerials discussed above in relation to FIG. 2.

The water tubes 26 are then joined together in a side by sidearrangement to form the inner wall of the gas conduit 12. The watertubes 26 may be in a helical or longitudinal or any other suitableconfiguration to form the inner wall of the gas conduit 12.

The heater 24 is adjacent to the water tubes 26 as shown in FIG. 3, tofacilitate heat transfer to the water in the tubes. Water within thewater tubes 26 may be heated by the heater 24 to aid in the productionof water vapour which migrates through the semi-permeable membraneportion and into the gas flow of the gas conduit 12. The wholearrangement may be encapsulated by an outer wall 20 which may also serveto provide structural support 18 or insulation while still allowing thegas conduit 12 to flex appropriately with patient movement.

FIGS. 4 and 5 illustrate another embodiment of the humidifying apparatusutilising a semi-permeable membrane portion 16 within a gas conduit 12where the direction of gas flow is given by the arrow 28. Thisembodiment of the humidification apparatus has a helical configurationfor the semi-permeable membrane portion 16, the structural reinforcingmember or members 18, the water channel 22 and the heating element 24.The helical configuration of the outer wall 20 may be similar toconventional conduits that are in common use in respiratory apparatus.Thus the humidification apparatus may be readily substituted intoexisting respiratory device by exchanging the gas conduit 12.

Alternatively it may be possible to insert the gas conduit 12 of thehumidification apparatus into an existing conventional conduit of arespiratory apparatus in order to upgrade the humidification performanceof a conventional respiratory apparatus.

For the above embodiments, the humidification apparatus may occupy oneor more sectors of the circumference of the inner wall of the gasconduit 12. In such a manner the semi-permeable membrane portion 16 thenoccupies only a portion of the inner wall of the gas conduit 12. Inaddition the portions of the inner wall formed by the semi-permeablemembrane portion 16 may be segmented along the length of the gas conduit12 inner wall.

The water supply to the water channel 22 or the water tubes 26 in theabove embodiments may comprise a single filling at the start of anovernight therapy session of CPAP for OSA, the volume of the waterchannel 22 or water tubes 26 being a sufficient water supply.

Alternatively a water reservoir (not shown) may be used, which may be anexternal reservoir or may form part of the gas conduit.

The water reservoir may be located in a portion of the outer wall 20 ofthe gas conduit 12. The location of the water reservoir along the gasconduit 12 may be at a suitable point along the conduit to allow gravityfeed or the use of micro-pump for the water supply.

Alternatively the water reservoir may be located with the PAP device 10where the connection for the water channels 22 and water tubes 26 to thewater reservoir is associated with the connection of the gas conduit 12to the PAP device 10. The water channels 22 or water tubes 26 may be ina loop arrangement so that water can be circulated through them and backto the water reservoir. Alternatively the water channels 22 or watertubes 26 may individually have an open end for water supply with theother end being closed, but may have a pore or perforation sufficient toallow gas to escape from the water channel 22 or water tube 26 as itfills or draws water.

Wick Embodiment

An alternative embodiment for the humidification apparatus is to use awick and/or capillary action device 30 within the gas conduit 12 asshown in cross-section in FIG. 6. In the following, references to “wick”includes the term “and/or capillary action”.

The wick device 30 has the ability to conduct water upon or within thewick device 30 such that water is available for vaporisation into thelumen 13 of the conduit. In addition a capillary action may also beinvolved within the wick device 30. An example of a suitable wick device30 is a material which is hydrophilic so that the water has a tendencyto spread across the extent of the material. Materials that may besuitable include cotton, activated perfluorinated polymer (e.g. “NAFION”stabilised perfluorosulfonic acid/PTFE copolymer by DuPont), polyestercopolymer (e.g. SYMPATEX polyester/polyether copolymer by SympatexTechnologies GmbH of Germany) and polyester fabrics (e.g. COOLMAXpolyester fabrics by Invista of USA). Alternatively a material may beimparted hydrophilic characteristics by using a particular liquid filmor the application of a gel or solid film.

The wick device 30 may have an internal structural form of a fabric (asshown in FIG. 6), sponge, a film, a bundle of fibres or a hydrophilicporous, flexible solid e.g. plastic, metal or ceramic. The external formof the wick device 30 may be a continuous liner upon the inner wall ofthe gas conduit 12 or in a strip form that is continuous or inlongitudinal segments or a helical arrangement about the inner wall ofthe gas conduit 12. An alternative embodiment may be the formation ofhydrophilic villi (not shown) along the inner wall of the gas conduit12, such hydrophilic villi serving to increase the area of interactionbetween the water film upon the hydrophilic villi and the gas in the gasconduit 12.

Alternatively the wick device 30 may be in the form of a very porousmembrane that may extend partially or wholly across the transverse crosssection of the gas flow path in the gas conduit 12, the material formingthe membrane being as per that described above for the wick.

A heater 24 for the wick device 30 may also be present as shown in FIG.6, having any one of the suitable forms described above.

Alternatively the wick device 30 may be wrapped partially or whollyaround a heater 24 that is secured to the inner wall of the gas conduit12.

The outer wall 20 and reinforcing 18 shown in FIG. 6 serve the functionsdescribed above for the semi-permeable membrane portion embodiments inFIGS. 2 to 5.

The water supply for the wick device 30 may be in the forms describedabove for the semi-permeable membrane portion 16, for example the use ofa single fill of water, a water reservoir either as a separate componentor co-located with the gas conduit 12 or with the PAP device 10.Alternatively one or more narrow, open-ended pipes, with or withoutperforations along the pipe length, may be used to supply water from awater reservoir to various locations along the wick device 30.

The wick device 30 has the advantage of self limiting the amount of freeliquid water in the gas conduit 12. Free liquid as large droplets orpuddles in the gas conduit 12 may be entrained into the gas flow,obstruct the gas conduit 12 or flow back into the PAP device 10. Howeverthe wick device 30 only draws as much liquid water as necessary to makea thin film across the wick device 30 and in addition any condensingwater may be transferred by the wick device 30 to other areas on thewick or to the water supply.

The wick device 30 embodiment of the humidification apparatus may alsobe of appropriate transverse cross-sectional dimensions to facilitateits substitution with conventional conduits or insertion intoconventional conduits for respiratory apparatus, as described above forthe semi-permeable membrane portion 16 humidifying apparatus.

Wick Within Water Channel

FIG. 8 schematically shows a cut-away perspective view of an alternativeembodiment of the humidification apparatus. A perforated wall 36 formsthe inner surface of the gas conduit 12 and is the boundary to the lumen13. The perforated wall 36 has many through holes 38 that may range inwidth from 0.2 micro-metres to 1 mm. If the smaller hole 38 sizes areused the perforated wall 36 may act as a semi-permeable membrane whichallows the passage of water vapour but not liquid water. About theperforated wall a helical winding of a structural support and spacer 18is present along the length of the gas conduit 12, in a fashion similarto that described for FIGS. 4 and 5. An outer wall 20 joins thestructural support and spacer 18 so that a water channel 22 is formedbetween the perforated wall 36 and the outer wall 20. The water channel22 proceeds up the length of the gas conduit 12 in a helical manner in asimilar manner to that described for FIGS. 4 and 5.

Within the water channel 22 a wick device 30 is wound about theperforated wall 36 as illustrated in FIG. 8. A heater 24 is also woundabout the perforated wall 36, adjacent to and in thermal contact withthe wick device 30. Alternatively the wick device 30 may be wrappedaround the heater 24 or form a sleeve about the heater 24. The wickdevice 30 and the heater 24 may be in any one of the forms describedabove. The wick device 30 draws water 40 from a water reservoir 42 andinto the water channel 22. The water is heated in the water channel 22by the heater 24 to generate vapour 44 (see FIG. 9) that moves throughthe holes 38 of the perforated wall 36 and into the gas which travelsthrough the lumen 13 in the direction shown by arrows 28.

In an alternative embodiment the structural support and spacer 18 withthe wick device 30 and heater 24 may be in a longitudinal arrangementalong the gas conduit 12. In yet another embodiment the structuralsupport and spacer 18 may be absent whilst the wick device 30 forms asleeve over an inner conduit formed by the perforated wall, with theouter wall 20 of the gas conduit enclosing the wick device 30 sleeve andthe heater 24.

FIG. 9 is a longitudinal cross-sectional view of FIG. 8 along the lines9-9, schematically illustrating the operation of the humidificationapparatus. When the wick device 30 is heated by the heater 24 watervapour 44 evaporates from the liquid water upon and/or within the wickdevice 30 and into the water channel 22. From the water channel 22 thewater vapour 44 moves through the holes 38 of the perforated wall 36 andinto the gas which travels through the lumen 13 in the direction shownby the arrows 28. Thus the water channel 22 in this embodiment containswater as a liquid and a substantial amount of water vapour. This is incontrast to the water channel 22 embodiments of FIGS. 2, 4 & 5 wheresubstantially less or no water vapour is present in the water channel22.

FIG. 10 schematically shows the humidification apparatus of the presentembodiment connected with the PAP device 10 and a cut-awayrepresentation of the water reservoir 42. The humidification apparatuswithin the gas conduit 12 is connected to the water reservoir 42 and theheater power supply 46 via a water supply pipe 48. The water reservoir42 is a sealed vessel that is pressurised by a pressurising pipe 50which is connected to the PAP device 10 and the gas conduit 12. In turnthe water channel 22 (FIGS. 8 & 9) is pressurised via the waterreservoir 42 through the connecting water supply pipe 48. The gaspressurisation of the water reservoir 42 and the water channel 22 to thesame pressure as the gas in the lumen 13 enables the water vapour 44generated in the water channel 22 to freely migrate and/or diffusethrough the perforated wall 36 and into the lumen 13. In an alternativeembodiment the pressurising pipe 50 is combined with the water supplypipe 48 such that initial pressurisation of the water channel 22 andwater reservoir 42 occurs through the perforated wall 36 from the lumen13. After initial pressurisation the pressure in the water channel 22 ismaintained and exceeded by the heated production of water vapour 44 fromthe wick device 30 and the heater 24.

In yet an alternative embodiment a device (not shown) for introducingadditional gas pressure into the water reservoir 42 is connected to thepressurising pipe 50. The additional gas pressure is used accelerate thewater vapour transfer from the water channel 22 to the lumen 13, sincethere will be a continuous gas flow from the water channel 22 into thelumen 13.

Additional Use of the Semi-Permeable Membrane

An alternate embodiment of all the embodiments of the humidificationapparatus described above includes the use of a semi-permeable membraneacross the transverse cross-section of lumen 13. Preferably thetransverse semi-permeable membrane (not shown) would be located close tothe patient mask 14, but may be located at another or multiple locationsalong the gas conduit 12. The purpose of the transverse semi-permeablemembrane is to prevent the passage of water droplets along the gasconduit 12 to the patient.

Another alternate embodiment of all the embodiments of thehumidification apparatus that use a semi-permeable membrane as describedabove, includes the use of a semi-permeable membrane that has multiplelayers (not shown). The layers of semi-permeable membranes differ intheir ability to repel liquid water (hydrophobicity), structuralstrength and ability to retain the precipitates of dissolved ions in theliquid water, for example Calcium Carbonates and various otherprecipitates commonly found in mineralised or “hard water”. The firstsemi-permeable membrane layer adjacent the liquid water may have theleast hydrophobicity but the greatest ability to retain the precipitatesas they are deposited in the process of water vaporisation through thesemi-permeable membrane layers. Consequently the first semi-permeablemembrane also has the greatest structural strength so that it does notfail with the accumulation of precipitates. Successive semi-permeablemembrane layers have increasing hydrophobic properties with reducingstructural strength. Thus the semi-permeable membrane layers act as agraded filter as well as a graded barrier to liquid water.

In another embodiment the multiple layer semi-permeable membrane mayalso be used across the transverse cross-section of lumen 13 asdescribed above. However in this embodiment the multiple layersemi-permeable membrane may also function as a graded filter for mucousand the like which may be introduced into the gas conduit 12 when thepatient exhales.

The humidification apparatus embodiments described above do not sufferfrom the problem of tilting and consequential spillage of water that aconventional tub humidifier is prone to. This is because the liquidwater is enclosed as in the case of the semi-permeable membrane portion16 or the liquid water is only present as a thin film as in the case ofthe wick device 30.

Segmentation of Humidification and Heating along the Gas Conduit

The humidification apparatus has been described above with itshumidification apparatus 16, 30 and heater 24 segmented in locationalong the gas conduit 12. The segmentation may be in the form ofmultiple separate segments of the humidification apparatus 16, 30 and/orwith the heater 24. Such an embodiment may produce humidity in one moresegments of the gas conduit 12, then in one or more other segments ofthe gas conduit 12 the condensate could be collected and thenre-vaporised with the heater 24.

The segmentation of the humidification apparatus 16, 30 and the heater24 may also be in time of operation for each segment of thehumidification apparatus. For example humidification may be timed to thepatient's inspiration, such that sufficient water vapour is deliveredinto the passing gas stream during inspiration to maintain a desiredhumidity. The level of humidity in the gas conduit may be regulated bythe use of a humidity sensor (not shown) and a gas flow sensor (notshown) to detect inspiration. The output of these sensors is then usedto control the level of heating with the heater and /or the supply ofwater to the humidification apparatus. The humidity sensor may belocated where-ever convenient along the gas conduit 12, most preferablyat some distance from the patient end of the gas conduit. The gas flowsensor may be located within the PAP device 10, gas conduit 12 or thepatient mask 14. The gas flow sensor may consist of a temperature sensorlocated near the patient end of the gas conduit 12 or in the patientmask 14. In such positions the patient's respiration cycle ofinspiration to respiration may be sensed by changes in the sensedtemperature.

Another example of timed operation of the humidification apparatus 16,30 and heater 24 is at a cold start-up in cold climates where it isdesirable to provide warm air to the patient firstly and then humidifiedwarm air. For a cold start-up: initially the humidification apparatus inthe conduit may not have water supplied to it so that when the heaterstarts there is no energy intensive heating of water and consequentlythe heating of the gas flow is rapid. Once the desired gas temperatureis obtained water is then supplied to the humidification apparatus tobegin humidification before the onset of adverse respiratory symptomsassociated with the breathing of low humidity air. The water may also besupplied at a slower controlled rate at the beginning of thehumidification.

Disposable

The materials and construction of all the above embodiments may be of acost and construction to make them disposable. Or in an alternativeembodiment the wick device 30 may be a removable liner and/or an insertthat may be replaced in the gas conduit 12.

Sterility

Sterilisation may be provided within the humidification apparatus tocounteract the growth and lodgement of disease causing agents within thehumidification apparatus. In one embodiment, this may include a methodand device to produce a sterilising temperature within the humidifyingapparatus, for example through the heater 24 described above. Analternative sterilisation may be by the use of a chemical treatment ofone or more surfaces or materials within the apparatus, for example thewick or semi-permeable membrane portion may be permanently impregnatedwith a chemical that inactivates viruses and arrests bacterial growth.Alternatively a sterilising fluid may be supplied to the humidificationapparatus 16, 30 instead of water, for a short period when thehumidification apparatus is not connected to the patient.

In another embodiment the semi-permeable membrane 16 and/or theperforated wall 36 may have a pore size less than 0.2 micrometressufficiently small to prevent the passage of viruses and bacteria fromthe water within the water channel 22 or water tubes 26 to the gaswithin the lumen 13. Alternatively the semi-permeable membrane 16 or theperforated wall 36 may have an adjacent membrane layer which performsthe function of preventing the passage of viruses and bacteria whilstallowing the free passage of water vapour.

In a further embodiment a sterile filter (not shown) may used across thetransverse cross-section of lumen 13. The sterile filter prevents thepassage of viruses and bacteria but allows the passage of gas and watervapour through the lumen 13. The sterile filter may be placed across thelumen 13 at the patient mask 14 end of the humidification apparatus orany other convenient location across the lumen 13.

In another embodiment the gas conduit 12 may contain an ultravioletlight device (not shown) within a portion of the length of the gasconduit 12. The ultraviolet light device illuminates all the gas andwater vapour within the lumen 13 and is of sufficient intensity andappropriate wavelength to inactivate all bacteria and viruses within thelumen 13. The ultraviolet light device portion of the gas conduit 12 maybe located at the patient mask 14 end of the humidification apparatus.

Gas Conduit Internal Wall Projections

For the above embodiments the internal wall of the gas conduit 12 mayhave projections (not shown) extending into the lumen 13. Theseprojections may serve to facilitate the turbulent mixing of the gasstream with the water vapour issued from the humidification apparatus16, 30 and hence promote faster humidification of the gas stream.Alternatively the projections may also contain extensions of thehumidification apparatus 16, 30. These projections may facilitate thetransfer of the water vapour from the humidification apparatus 16, 30located at the slow boundary layer of the gas flow at the wall of lumen13, to the faster and more turbulent gas flow in the body of the lumen13.

The humidification apparatus embodiments described above have theadvantage of presenting a large area of interaction between the gas flowstream and the water compared to that for a conventional water tubhumidifiers. In addition the present humidification apparatus inventionis compact and incorporated unobtrusively within the gas conduit 12 tothe patient. The gas conduit 12 may have a flexibility which iscomparable to that of a conventional conduit in the prior art. Inaddition there is minimal impedient to the gas flow or to the desirableacoustic monitoring from the patient mask 14 through the gas conduit 12

Although the invention has been herein shown and described in what isconceived to be the most practical and preferred embodiments, it isrecognized that departures can be made within the scope of theinvention, which is not to be limited to the details described hereinbut is to be accorded the full scope of the appended claims so as toembrace any and all equivalent assemblies, devices and apparatus.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise, comprised and comprises where they appear.

It will further be understood that any reference herein to known priorart does not, unless the contrary indication appears, constitute anadmission that such prior art is commonly known by those skilled in theart to which the invention relates.

1. A humidifier in the form of a flexible, tubular gas conduit andcomprising: a first portion configured to convey gas through thehumidifier, the first portion comprising a central lumen that is open ata first end and at a second end; a second portion surrounding the firstportion and positioned to be outside a flow of any gas conveyed throughthe humidifier, the second portion comprising a liquid water retainerand a heater configured to vaporize liquid water retained within theliquid water retainer; and a flexible outer wall housing the first andsecond portions.
 2. A humidifier according to claim 1, wherein thecentral lumen is defined by a flexible, gas permeable inner wallconfigured to facilitate a flow of water vapour from the liquid waterretainer to the central lumen.
 3. A humidifier according to claim 2,wherein the gas permeable inner wall is configured to prevent a flow ofliquid water from the liquid water retainer to the central lumen.
 4. Ahumidifier according to claim 1, wherein the heater is positioned insidethe liquid water retainer and comprises a plurality of heating elementsextending along the length of the liquid water retainer.
 5. A gasconduit according to claim 4, wherein the plurality of heating elementsdefine a plurality of channels configured to receive a flow of waterfrom a water inlet.
 6. A humidifier according to claim 1, wherein theliquid water retainer comprises a plurality of water tubes forming oneor more portions of a flexible, gas permeable inner wall defining thecentral lumen.
 7. A humidifier according to claim 1, wherein the liquidwater retainer comprises at least one wick and/or capillary actiondevice.
 8. A respiratory apparatus configured to provide positivepressure gas to a patient's airways, the respiratory apparatuscomprising: a positive airway pressure device configured to generate aflow of positive pressure gas; a patient interface configured to engagethe patient's face and be in communication with the patient's airways;and a humidifier according to claim 1, the humidifier being configuredto convey the flow of positive pressure gas to the patient interface. 9.A respiratory apparatus according to claim 8, wherein the positiveairway pressure device comprises a liquid water reservoir configured tosupply water to the liquid water retainer.
 10. A respiratory apparatusaccording to claim 9, wherein the liquid water reservoir and the liquidwater retainer are configured to be in a loop arrangement so that liquidwater is circulated between the liquid water retainer and the liquidwater reservoir.
 11. A humidifier configured to humidify and convey aflow of respiratory gas, the humidifier being in the form of a flexible,tubular gas conduit and comprising: an air inlet, an air outlet and acentral lumen extending from the air inlet to the air outlet, thecentral lumen being configured to convey the flow of respiratory gas toa patient's airways; a liquid water retainer configured to retain liquidwater, the liquid water retainer being closed at a first end and havinga liquid water inlet at a second end; and a heater configured to heatthe liquid water in the liquid water retainer to generate water vapor.12. A humidifier according to claim 11, wherein the central lumen isdefined by a flexible, gas permeable inner wall configured to facilitatea flow of water vapour from the liquid water retainer to the centrallumen.
 13. A humidifier according to claim 12, wherein the gas permeableinner wall is configured to prevent a flow of liquid water from theliquid water retainer to the central lumen.
 14. A humidifier accordingto claim 11, wherein the heater is positioned inside the liquid waterretainer and comprises a plurality of heating elements extending alongthe length of the liquid water retainer.
 15. A gas conduit according toclaim 14, wherein the plurality of heating elements define a pluralityof channels configured to receive a flow of water from the liquid waterinlet.
 16. A respiratory apparatus configured to provide positivepressure gas to a patient's airways, the respiratory apparatuscomprising: a positive airway pressure device configured to generate aflow of positive pressure gas; a patient interface configured to engagethe patient's face and be in communication with the patient's airways;and a humidifier according to claim 11, the humidifier being configuredto convey the flow of positive pressure gas to the patient interface.17. A respiratory apparatus according to claim 16, wherein the positiveairway pressure device comprises a liquid water reservoir configured tobe connected to the liquid water inlet and supply water to the liquidwater retainer.
 18. A respiratory apparatus according to claim 17,wherein the liquid water reservoir and the liquid water retainer areconfigured to be in a loop arrangement so that liquid water iscirculated between the liquid water retainer and the liquid waterreservoir.
 19. A humidifier configured to humidify and convey a flow ofrespiratory gas, the humidifier being in the form of a flexible, tubulargas conduit and comprising: a central lumen open at a first end and at asecond end, the central lumen being configured to convey the flow ofrespiratory gas to a patient's airways; a liquid water retainerconfigured to retain liquid water, the liquid water retainer beinglocated outside any flow of respiratory gas; and a heater configured toheat the liquid water in the liquid water retainer to generate watervapor.
 20. A respiratory apparatus configured to provide positivepressure gas to a patient's airways, the respiratory apparatuscomprising: a positive airway pressure device configured to generate aflow of positive pressure gas; a patient interface configured to engagethe patient's face and be in communication with the patient's airways;and a humidifier according to claim 19, the humidifier being configuredto convey the flow of positive pressure gas to the patient interface.